If you step on a piece, it ruins your day. If you find a chunk under your desk, it’s time to squeal. But in San Luis Obispo, California, it’s perfectly OK to chew a big hunk of chicle and stick it on the walls of Bubblegum Alley. There are even several gumball machines right outside the alley’s entrance to gather up a plethora of gumballs before entering.

Bubblegum Alley, thought by the city’s historical society to have been created by high school students in the ‘50s, is a chewy, multicolored mess of thousands upon thousands of pieces of gum, measuring 70 feet long and 15 feet high. The alley, which from the inside looks like an amorphous blob, is located right off of the city’s main street and situated in the middle of downtown.

“Bubblegum Alley is a must-see in SLO because it’s not every day you can see an entire walkway lined with gum,” says Becca Norman, a San Luis Obispo resident who runs a blog dedicated to the city. “There’s a fair amount of bubblegum art, like the large mural of a guy blowing a bubble.”

People usually just stick their chewed gum directly on the wall, but like Norman tells mental_floss, some leave their mark a little more uniquely. Aside from the typical “Hi,” the wall has been the home to numerous murals, “Just Married” announcements, and brief goodbye messages from students at Cal Poly, a polytechnic university in the city.

Norman says the whole gum thing is mostly a tourist attraction.

“Tourists always find the alley a lot more interesting than the locals,” she says. “Kids and teenagers think it’s cool, and parents think it’s unsanitary. A lot of people just ignore it unless they are with out-of-town guests. Still, everyone considers Bubblegum Alley an attraction because it’s one of the few things that people hear most about the city.”

The alley has even appeared on ABC’s Ripley’s Believe It or Not and E!’s The Girls Next Door, and was mentioned on Showtime’s United States of Tara. TheLos Angeles TimesandNew York Timesare just a few of the major media outlets that have showcased the brick space.

In a video posted by the Wall Street Journal, Bobby Berryman, the owner of local eatery Enzo’s East Coast Eatery—located on the other side of one of the gum-covered walls—says that the gum has formed a hefty layer on the alley’s walls. And it hasn't been cleaned since the 70s, according to Norman. Deborah Holley, an administrator of the Downtown Association, told the Los Angeles Times that when the fire department hosed the alley down one year, the result wasn’t pretty: Instead of falling off the walls and hitting the ground, thousands of pieces of chewed gum were blasted high into the air and rained down on people nearby. They ran waving their arms from a gum-storm that day, Holley said.

Over the years, San Luis Obispo residents have wavered on their opinions toward the icky tradition, coming together every now and then to campaign for its removal. Still, the city’s Chamber of Commerce lists the alley as a “special attraction” and Enzo’s even has a display of the alley’s history. Norman thinks it’s here to stay.